Thermoablation is used in the treatment of tumorous bones. However, little is known about the influence such thermal treatment has on the mechanical properties of bone tissue. The purpose of this work was to study the influence of thermal treatment in a range of 60–100 °C (in increments of 10 °C) on the structural properties of pig femurs using an original approach that involved a periosteal arrangement of heating elements providing gradual dry heating of the bone from its periphery to its center. Heating of freshly extracted bone tissue segments was performed ex vivo using surface heaters of a Phoenix-2 local hyperthermia hardware system. Mechanical testing followed the single-axis compression scheme (traverse velocity of 1 mm/min). In the 60–90 °C range of heating, no attributes of reduced structural characteristics were found in the samples subjected to thermoablation in comparison to the control samples taken from symmetric areas of adjacent cylinders of healthy bones and not subjected to heat treatment. The following statistically significant changes were found as a result of compressing the samples to 100 °C after the heat treatment: reduced modulus of elasticity and increased elastic strain (strain-to-failure), mainly due to increases in plastic deformation. This finding may serve as evidence of a critical ex vivo change in the biomechanical behavior of bone tissues at such temperatures. Thus, ex vivo treatment of bone tissue in the thermal range of 60–90 °C may be used in studies of thermoablation efficiency against tumor involvement of bones.
Purpose: to study the changes in the temperature outside and inside the long tubular bones of animals under the influence of different temperature regimes for a given time.Material and Methods. The experiments were conducted using fresh frozen pig long bones. The heating was carried out using surface heaters, the temperature of which was determined by the selected mode for 1 hour; fixation of temperature values was carried out every minute. Four heating modes were used: 3 modes of constant heating (60, 70, 80 °C) and the maximum heating mode, in which no special temperature limit was set, so heating was carried out up to 120 °C.Results. During the first 10 min of heating, a rapid rise in temperature occurred. The temperature increase rate on the outer surface outstripped the temperature increase rate on the inner surface of the bone, thus leading to a significant temperature difference. Further, there was a slowdown in the rate of temperature increase, which led to a gradual convergence of the temperature values inside and outside the bone, followed by temperature stabilization at a stable level (plateau), which was different for the studied areas. During this period, the temperature difference was 3.5–6 °C and it remained at this level until the end of the study. At a constant heating mode (60/70/80 °C), temperature stabilization occurred at the level of 55/61/70 °C in the center of the medullary canal and at the level of 58/67/75 °C under the heater, respectively. The period before reaching the stabilization temperature was 30–40 min. The stable temperature levels both inside and outside the bone were below the temperature stabilization level of the heater. Therefore, to achieve the planned temperature in the center of the bone to its outer surface, it is necessary to apply a high temperature, i.e., a downward temperature gradient is formed: the heater stabilization temperature – the temperature on the outer surface – the temperature inside the medullary canal. Increasing the exposure temperature can shorten the heating period, but increase the temperature difference during the heating period (up to 25 °C in the fifth minute of heating when using the maximum heating mode).Conclusion. To ensure reaching the required temperature (60°C) within a short time (15–20 min) while maintaining optimal temperature parameters, it was proposed to develop variable temperature modes that would combine the initial use of the maximum heating mode until reaching the desired temperature in medullary cavity, followed by switching to a constant temperature mode, which allowed maintaining the achieved temperature level during therapeutic exposure.
This research focused on studying regularities in changes in strength characteristics and histological patterns of healthy tubular bone tissue depending on the temperature setting of hyperthermal treatment. Experimentation has established that heating the experimental bone sample in a temperature range of 60 to 70 °C does not cause any decline in strength characteristics compared to the control samples not subject to heat treatment. In compression tests (along the length of the bone), after heating the bone samples ex vivo to 80 °C, the strength characteristics were found to increase as the samples sustained a higher maximum stress. In bending tests, in contrast, the strength characteristics were reliably found to decrease in bone samples at 80 °C and 90 °C for the maximum stress indicator and 90 °C for the modulus of elasticity. Data obtained through histological examination further demonstrated statistically significant differences between the two temperature ranges of 60–70 °C and 80–90 °C, where semi-quantitative assessment revealed statistically significant differences in the markers of bone tissue destruction caused by hyperthermal treatment. Moderate (at 60–70 °C) and pronounced (at 80–90 °C) dystrophic and necrotic changes were observed both in the cells and the intercellular matrix of the tibia. From a practical point of view, the temperature range of 60–70 °C can be considered operational for thermal ablation since, at these temperatures, no statistically significant decline was observed for the strength characteristics in either the cross-section or length-section.
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